1. Field of the Invention
This invention relates generally to providing die interconnection within a semiconductor die and, more specifically, to a method and apparatus for routing die interconnections for accessing selected functional segments located on an integrated circuit semiconductor die.
2. State of the Art
A typical integrated circuit (IC) or semiconductor die includes external connection points termed “bond pads” that are in electrical communication with integrated circuits formed on the active surface of the semiconductor die. The bond pads are used to provide electrical connection between the integrated circuits and external devices, such as a lead frame or a printed circuit board. The bond pads also provide sites for electrical testing of the die, typically by contact with probes, which send and receive signals to and from the die to evaluate the functionality of the die.
In a conventional semiconductor die and lead frame assembly, the semiconductor die is attached to a die paddle of a lead frame using an adhesively coated tape or an adhesive, in some instances. The bond pads formed on the active surface (face) of the die are typically electrically and mechanically attached to lead fingers of a lead frame either terminating adjacent the periphery of the semiconductor die, if it is a conventional lead frame, or adjacent the center of the semiconductor die, if it is a lead-over-chip type lead frame, using bonding wires of gold, aluminum or other metals or alloys thereof.
Wire bonding is typically a process through which some or all of the bond pads formed on the active surface of the die are connected to the lead fingers or buses of a lead frame by metal bonding wires. The bonding wires comprise the electrical bridge between the bond pads and the leads of the packaged integrated circuit. A wire bonding apparatus bonds the bonding wires to the bond pads and to the lead fingers of the lead frame, typically using heat and pressure, as well as ultrasonic vibrations in some instances. Following wire bonding, the lead frame and die are typically encapsulated in a suitable plastic (particle-filled polymer) or, in some instances, packaged in a preformed ceramic or metal package. After encapsulation, the lead fingers of the lead frame are trimmed and configured to form the desired external leads of a completed semiconductor package in what is termed a “trim and form” operation.
It is often desirable to interconnect various bond pads on a single semiconductor die in order to alter the input or output functionality, or both, of the semiconductor die, such as when it is necessary to “wire around” defective portions of a semiconductor die that are only partially functional. For example, a 16 megabit DRAM memory die may only demonstrate 11 megabits of functional memory under electrical testing and burn in. Alternatively, it may be desirable for a semiconductor die having a given input/output (I/O) bond pad configuration to “look” to a particular lead frame or carrier substrate as if it were configured differently so that the semiconductor die could be used with a lead frame for which it was not originally intended. Such “wire around” functions, where possible, are typically accomplished by interconnecting bond pads on the semiconductor die through external circuitry in printed circuit boards or other carrier substrates to which the semiconductor die is mounted. Where the desired input or output, or both, functionality configuration varies from one semiconductor die to another, a separately configured printed circuit board or other carrier substrate must be provided for each desired input or output, or both, functional configuration. Thus, it would be desirable to provide a relatively easy way of interconnecting selected bond pads on a single integrated circuit semiconductor die without requiring the use of external circuitry imprinted circuit boards and other carrier substrates.
One solution has been to add electrically isolated intermediate connection elements or wire bondable jumper pads attached to the active surface of the die. These bondable jumper pads are electrically isolated from the external circuitry and from the circuitry of the semiconductor die, but for wire bonds extending to or from, or both, the bondable jumper pad. More specifically, each bondable jumper pad is not directly electrically connected to the internal circuitry of the semiconductor die, unlike the bond pad, but provides a “stepping stone” for wire bonds between bond pads of the semiconductor die or between a bond pad and a conductor external to the semiconductor die. Thus, a relatively short wire bond can be formed from a bond pad to the jumper pad and another relatively short wire bond from the jumper pad to another bond pad (or external conductor) forming an electrical connection between the bond pads (or bond pad and external conductor).
In another solution, a plurality of jumper pads is provided over the active surface of the semiconductor die, thus providing various serial jump points for a plurality of wire bonds to be formed in series between a plurality of bond pads. Where the semiconductor die has bond pads located about a peripheral edge of the active surface, a grid or array of jumper pads may be provided proximate the center of the active surface and at least partially bounded by the periphery bond pads.
Although these bond pads are provided as alternative interconnections to provide wire around defective portions, additional functionality is desired to be accessed with various options being implemented on an integrated circuit semiconductor die. In certain situations, it is desirable to modify various circuits on the integrated circuit semiconductor die in such a way as to achieve a particular result. For example, in FIG. 1, a circuit design 2 is depicted that includes a regulator 4. Regulator 4 can be optioned in for a 5 volt (V) application and, with the addition of a metal masking step, can be optioned out for a 3.3 V application. Regulator 4 is tied to the gate of a field effect transistor 6, which is utilized as a pass device, that is controlling an external VCCX power signal and an internally regulated VCCR power signal. With a metal mask 9, or a fuse integrated into the integrated circuit, regulator 4 can be bypassed as is shown in FIG. 2. Through the use of a fuse option or the metal mask 9 option, the gate of transistor 6 is hard wired at node 8 to Vss, and metal mask 9 is still used to short the source and drain of field effect transistor 6 in order to avoid a voltage drop of several hundred millivolts across the transistor 6.
In another situation, as shown in FIG. 3, there is an assembly limitation of the number of bonds that could be made to a single lead finger for a particular design lead frame. FIG. 3 shows a plurality of lead fingers 12 that is aligned on the perimeter of a particular semiconductor die 10. The lead fingers 12 are connected to a portion of the plurality of bond pads 14, where multiple pads are bonded to particular lead fingers 12. For example, such as illustrated in FIG. 2 where a design would require multiple connections between VCC and VSS to be bonded multiple times, a limited number of pins are available. Thus, it would be desirable to interconnect selected bond pads 14 on a single integrated semiconductor die without requiring the use of external circuitry in printed circuit boards and other carrier substrates or extraneous masking steps dedicated solely for element interconnection apart from other masking steps.